Method of screening for ligands to a receptor-type tyrosine kinase

ABSTRACT

PCT No. PCT/AU92/00294 Sec. 371 Date Apr. 18, 1994 Sec. 102(e) Date Apr. 18, 1994 PCT Filed Jun. 19, 1992 PCT Pub. No. WO93/00425 PCT Pub. Date Jan. 7, 1993The present invention relates to a method of screening for ligands to a receptor-type tyrosine kinase. The receptor-type tyrosine, in its naturally occurring form, is characterized by being reactive to monoclonal antibody III.A4, having an apparent molecular weight of approximately 120-150 kD in its glycosylated form, and having the N-terminal amino acid sequence E L I P Q P.

The present invention relates generally to a novel receptor-type tyrosine kinase and to genetic sequences encoding same.

Tyrosine kinases form an important class of molecules involved in the regulation of growth and differentiation (1). One mode of proof for this role came from the identification of receptors which bind known soluble growth factors. The receptors for epidermal growth factor (EGF) (2), platelet derived growth factor (PDGF) (3) and colony stimulating factor-1 (CSF-1)(4) were all shown to be transmembrane molecules with the cytoplasmic regions encoding a tyrosine kinase catalytic domain. The CSF-1 receptor is homologous to the PDGF receptor in both the catalytic and extracellular domains (1,5). The extra cellular domain of these proteins is distinguished from other tyrosine kinases by the presence of immunoglobulin-like repeats (1,6). Based on structural properties of the kinase domain, the c-kit protein was identified as another member of this family (7). The c-kit gene locus appears to underpin the defects in the congenitally anaemic W/W mouse (8-10). The ligand has now been identified (11-14) as shown to be encoded by the Sl locus. The locus is abnormal in the Steel mouse (15) which has identical defects to the W/W mouse but encodes a normal c-kit gene.

The other line of evidence for a critical role of tyrosine kinase proteins in growth control came from the study of vital oncogenes (16-17). These genes were shown to be directly involved in growth dysregulation by observations of a change in cell growth following introduction of DNA encoding these genes into fibroblasts. All oncogenes have been shown to have close cellular homologues (proto-oncogenes). One of the first identified oncogenes was v-src, the cellular homologue (c-src) is the prototypical representative of the family of cytoplasmic tyrosine kinases which, following myristylation, become associated with the inner leaf of the cell membrane (18). Within the haemopoietic system a number of lineage-restricted src-like kinases have been defined (19).

The T cell-associated src-like kinase, lck, has been shown to associate independently with both the CD4 and CD8 transmembrane glycoproteins to form a signalling complex (20,21). By contrast, v-erb-B and v-fms, like their cellular homologues the EGF receptor and CSF 1 receptor, respectively, are transmembrane molecules encoding the entire signal transduction machinery in a single polypeptide (1,17).

Detailed analysis of the amino acid sequences of these proteins has revealed conserved structural motifs within the catalytic domains (5). Both tyrosine and serine-threonine kinases have a consensus GXGXXG sequence (SEQ ID NO:12) which is found in many nucleotide binding proteins (5). Other conserved sequence motifs are shared by both types of kinase while others are specific for the tyrosine or the threonine-serine kinase subgroups (5). The tyrosine kinases, while having regions of sequence conservation specific to this family, can be further subdivided according to the structural features of the regions 5' to the catalytic domain (1,4-7). The novel tyrosine kinase of the present invention exhibits the same general characteristics as previously known tyrosine kinases.

In accordance with the present invention, a new receptor-type tyrosine kinase is provided and which is identified as a member of the eph/elk family of tyrosine kinases (22,23). The novel tyrosine kinase receptor is designated HEK ("human eph/elk-like kinase"). As the present inventors have identified expression of HEK in both pre-B and T cell lines, the receptor molecule of the present invention and/or its ligand is contemplated herein to have particular applicability for use as agents in the in vivo modulation of the production and/or function of pre-B, B and T cells.

Accordingly, one aspect of the present invention provides an isolated receptor-type tyrosine kinase, said tyrosine kinase characterised by, in its naturally occurring form, being reactive to the monoclonal antibody III.A4, having an apparent molecular weight of approximately 120-150 kD in the glycosylated form and having an N-terminal amino acid sequence SEQ ID No:1 comprising:

    E L I P Q P.

Preferably, the tyrosine kinase has an N-terminal amino acid sequence SEQ ID NO:2 comprising:

    E L I P Q P S N E V N L X D,

wherein X is any amino acid and is preferably L.

More preferably, the tyrosine kinase has an N-terminal amino acid sequence comprising the amino acids:

    E L I P Q P S N E V N L X D (S) K X.sup.1 I Q, SEQ ID NO:3

wherein X and X¹ are any amino acid and preferably L and T, respectively.

Even more preferably, the tyrosine kinase comprises the amino acid sequence set forth in FIG. 1 or any parts or portions thereof, or having an amino acid sequence with at least 30% homology to the amino acid sequence set forth in FIG. 1 and having the identifying characteristics of HEK. More preferably, the degree of homology is at least 40%, still more preferably at least 55, even more preferably at least 70% and still even more preferably greater than 80%.

The hybridoma producing the monoclonal antibody III.A4 was deposited at Public Health Laboratory Service, European Collection of Animal Cell Cultures, Porton Down Salisbury, UK, on 20 Jun., 1991 under accession number 91061920.

The term "isolated" as used in relation to the tyrosine kinase of the present invention includes a biologically pure preparation comprising at least 20%, preferably at least 40%, more preferably at least 60% and even more preferably at least 80% of the protein relative to other molecules as determined by weight, activity or other convenient means. The term also encompasses any form of the protein not in the naturally occurring state such as, but not limited to, a preparation of membranes containing the protein, a preparation of the protein separate from the membrane or a supernatant fluid comprising said protein. The preparation may be glycosylated, partially unglycosylated or complete unglycosylated or may have a glycosylation pattern altered from what is naturally occurring.

The tyrosine kinase of the present invention is expressed on a number of tumours of human origin. In particular, data are presented herein showing HEK expression in human lymphoid tumour cell lines LK63, Lila-1, JM, MOLT4 and HSB-2 and the human epithelial tumour HeLa. One skilled in the art, however, will immediately recognise that similar or homologous kinases may exist on non-tumour cells or on non-human tumours and which have similar properties to the tyrosine kinase of the present invention. For example, the results contained herein show some expression of HEK in heart muscle. Accordingly, the present invention extends to a tyrosine kinase functionally and structurally similar in any or all respects to the tyrosine kinase herein described including a kinase of non-tumour origin.

The present invention extends to preparations comprising the naturally occurring form of the tyrosine kinase protein, including any naturally occurring derivative forms thereof, as well as to synthetic and recombinant forms of the protein including any single or multiple amino acid substitutions, deletions and/or insertions to the polypeptide portion of the kinase and to analogues and homologues thereof. Such amino acid alterations to the molecule are examples of recombinant or synthetic mutants and derivatives of the kinase.

Insertions include amino acid and/or carboxyl terminal fusions as well as intra-sequence insertions of single or multiple amino acids. Generally, insertions within the amino acid sequence will be smaller than amino or carboxyl terminal fusions, of the order of say 1 to 4 residues. Insertional amino acid sequence variants are those in which one or more amino acid residues are introduced into a predetermined site in the protein. Deletional variants are characterised by the removal of one or more amino acids from the sequence. Substitutional variants are those in which at least one residue in the sequence has been removed and a different residue inserted in its place. Such subsitutions generally are made in accordance with the following Table 1.

                  TABLE 1                                                          ______________________________________                                         Original Residue  Exemplary Substitutions                                      ______________________________________                                         Ala               Ser                                                          Arg               Lys                                                          Asn               Gln; His                                                     Asp               Glu                                                          Cys               Ser                                                          Gln               Asn                                                          Glu               Asp                                                          Gly               Pro                                                          His               Asn; Gln                                                     Ile               Leu; Val                                                     Leu               Ile; Val                                                     Lys               Arg; Gln; Glu                                                Met               Leu; Ile                                                     Phe               Met; Leu; Tyr                                                Ser               Thr                                                          Thr               Ser                                                          Trp               Tyr                                                          Tyr               Trp; Phe                                                     Val               Ile; Leu                                                     ______________________________________                                    

Generally amino acids are replaced by other amino acids having like properties, such as hydrophobicity, hydrophilicity, electronegativity, bulky side chains, etc.

Amino acid substitutions are typically of single residues; insertions usually will be on the order of about 1-10 amino acid residues; and deletions will range from about 1-20 residues. Deletions or insertions preferably are made in adjacent pairs, i.e.: a deletion of 2 residues or insertion of 2 residues.

The amino acid variants referred to above may readily be made using peptide synthetic techniques well known in the art, such as solid phase peptide synthesis (Merrifield; J. Am. Chem. Soc., 85: p2149, 1964) and the like, or by recombinant DNA manipulations. Techniques for making substitution mutations at predetermined sites in DNA having known sequence are well known, for example M13 mutagenesis. The manipulation of DNA sequences to produce variant proteins which manifest as substitutional, insertional or deletional variants are well known in the art and are described for example in Maniatis et al (Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory, 1982).

Other examples of recombinant or synthetic mutants and derivatives of the tyrosine kinase protein of this invention include single or multiple substitutions, deletions and/or additions to any molecule associated with the kinase such as carbohydrates, lipids and/or proteins or polypeptides. Furthermore, it is possible that the tyrosine kinase protein of the present invention is a genetically altered version of a similar protein on normal cells. The present invention, therefore, extends to the tyrosine kinase protein from tumour or non-tumour origin and to all genetically altered forms thereof.

The terms "analogues" and "derivatives" extend to any functional chemical equivalent of the tyrosine kinase protein characterised by its increased stability and/or efficacy in vivo or in vitro. The terms "analogue" and "derivatives" also extend to any amino acid derivative of the tyrosine kinase protein as described above.

Analogues of HEK contemplated herein include, but are not limited to, modifications to side chains, incorporation of unnatural amino acids and/or derivatising the molecule and the use of crosslinkers and other methods which impose conformational constraints on the peptides or their analogues. Examples of side chain modifications contemplated by the present invention include modifications of amino groups such as by reductive alkylation by reaction with an aldehyde followed by reduction with NaBH4; amidination with methylacetimidate; acylation with acetic anhydride; carbamoylation of amino groups with cyanate; trinitrobenzylation of amino groups with 2, 4, 6 trinitrobenzene sulphonic acid (TNBS); acylation of amino groups with succinic anhydride and tetrahydrophthalic anhydride; and pyridoxylation of lysine with pyridoxal-5'-phosphate followed by reduction with NaBH₄.

The guanidino group of arginine residues may be modified by the formation of heterocyclic condensation products with reagents such as 2,3-butanedione, phenylglyoxal and glyoxal.

The carboxyl group may be modified by carbodiimide activation via O-acylisourea formation followed by subsequent derivitisation, for example, to a corresponding amide.

Sulphydryl groups may be modified by methods such as carboxymethylation with iodoacetic acid or iodoacetamide; performic acid oxidation to cysteic acid; formation of a mixed disulphides with other thiol compounds; reaction with maleimide, maleic anhydride or other substituted maleimide; formation of mercurial derivatives using 4-chloromercuribenzoate, 4-chloromercuriphenylsulphonic acid, phenylmercury chloride, 2-chloromercuri-4-nitrophenol and other mercurials; carbomoylation with cyanate at alkaline pH.

Tryptophan residues may be modified by, for example, oxidation with N-bromosuccinimide or alkylation of the indole ring with 2-hydroxy-5-nitrobenzyl bromide or sulphenyl halides. Tyrosine residues on the other hand, may be altered by nitration with tetranitromethane to form a 3-nitrotyrosine derivative.

Modification of the imidaxole ring of a histidine residue may be accomplished by alkylation with iodoacetic acid derivatives or N-carbethoxylation with diethylpyrocarbonate.

Examples of incorporating unnatural amino acids and derivatives during protein synthesis include, but are not limited to, use of norleucine, 4-amino butyric acid, 4-amino-3-hydroxy-5-phenylpentanoic acid, 6-aminohexanoic acid, t-butylglycine, norvaline, phenylglycine, ornithine, sarcosine, 4-amino-3-hydroxy-6-methylheptanoic acid, 2-thienyl alanine and/or D-isomers of amino acids.

Crosslinkers can be used, for example, to stabilise 3D conformations, using homo-bifunctional crosslinkers such as the bifunctional imido esters having (CH₂)_(n) spacer groups with n=1 to n=6, glutaraldehyde, N-hydroxysuccinimide esters and hetero-bufinctional reagents which usually contain an amino-reactive moiety such as N-hydroxysuccinimide and another group specific-reactive moiety such as maleimido or dithio moiety (SH) or carbodiimide (COOH). In addition, peptides could be conformationally constrained by, for example, incorporation of C.sub.α and N.sub.α -methylamino acids, introduction of double bonds between C.sub.α and C.sub.β atoms of amino acids and the formation of cyclic peptides or analogues by introducing covalent bonds such as forming an amide bond between the N and C termini, between two side chains or between a side chain and the N or C terminus.

The present invention, therefore, extends to peptides or polypeptides and amino acid and/or chemical analogues thereof having the identifying characteristics of HEK as broadly described herein, and/or to regions thereof capable of, or responsible for, its action in transducing signals or in stimulating cellular responses such as growth and/or differentiation.

Accordingly, reference herein to the receptor-type tyrosine kinase of the present invention includes the naturally occurring molecule, recombinant, synthetic and analogue forms thereof and to any mutants, derivatives and human and non-human homologues thereof. All such kinases are encompassed by the term "HEK".

The present invention further extends to the ligand for the novel receptor-type tyrosine kinase described herein and to any agonists and antagonists (e.g. soluble form of the receptor) of the enzyme. Since the tyrosine kinase is an oncogenic protein, antagonists to the receptor are of particular relevance and fall within the scope of the present invention. Such antagonists include antibodies (monoclonal and polyclonal), the enzyme itself in soluble form or otherwise, specific peptides, polypeptides or proteins and carbohydrates, amongst others. These types of antagonists are useful in developing anti-tumour agents where the growth or maintenance of the tumour itself is supported by the tyrosine kinase of the present invention. Accordingly, the addition of an effective amount of an antagonist to the tumour-associated receptor-type tyrosine kinase will inhibit, reduce or otherwise interfere with the receptor activity of the protein and thus prevent, reduce and/or inhibit tumour growth. The present invention, therefore, extends to pharmaceutical compositions comprising one or more antagonists to the tyrosine kinase herein described and one or more pharmaceutically acceptable carriers and/or diluents.

Ligand(s) for HEK are capable of being screened for in a number of ways. In one protocol, an expression vector (e.g. AP-TAG-HEK) is selected which encodes the entire extracellular region of HEK fused to an appropriate reporter molecule like alkaline phosphatase. The fusion protein expressed in cells is recovered from cell supernatants and used to stain (using the reporter molecule) tissue sections using the methods as described by Flanagan and Leder (39), the disclosure of which is incorporated herein by reference. For example, the fusion protein is incubated with cells suspected of bearing the ligand under conditions whereby the fusion protein forms a complex with the cell-bound ligand. The cells are washed to remove unbound fusion protein, and then assayed for reporter activity. Once cellular sources of ligand are identified these cells are then used to construct an expression library. If the ligand is cell bound (eg membrane bound), the expression vector (eg AP-TAG-HEK) is used to stain pools to search for positive clones. If the HEK ligand is secreted, then another strategy will be required. In this case, supernatants of pools can be used to screen for induction of HEK phosphorylation in LK63 or HEK transfectants. Alternatively, supernatants from tissues producing HEK ligand can be used as a source in affinity purification on columns to which the product of, for example, pEE14-HEK is linked as a specific absorbent. The sequence of the purified ligand will be determined and this information used to clone the HEK ligand from cDNA libraries.

Another aspect of the present invention is directed to a nucleic acid isolate comprising a sequence of nucleotides encoding the novel receptor-type tyrosine kinase (including its recombinant, synthetic, mutant, derivative, analogue and homologue forms). The nucleic acid sequence may comprise deoxyribonucleotides or ribonucleotides and may exist in single or double stranded form, alone or in combination with a vector or expression vector molecule. The nucleic acid may be naturally occurring RNA or DNA or may be cDNA including complementary forms thereof. The nucleic acid molecule may also contain single or multiple nucleotide substitutions, deletions and/or additions relative to the nucleotide sequence encoding the naturally occurring or recombinant form of the protein. The vectors containing the nucleic acid sequences of the present invention may replicate in eukaryotes and/or prokaryotes and contain promoter sequences capable of expression in one or both of these types of cells. Suitable cells include mammalian, insect, yeast and/or bacterial cells. Particularly preferred cell types include CHO, baculovirus and E. coli cells. The preferred nucleotide sequence comprising HEK is set forth in FIG. 1. The general techniques of recombinant DNA technology, including isolation of recombinant proteins, are well known and are described for example in Maniatis et al (Supra).

This invention also provides a transgenic cell or cell culture carrying a nucleic acid isolate as described above.

In another aspect, this invention provides a pharmaceutical composition comprising a soluble form of the receptor-type tyrosine kinase as broadly described herein, said composition further comprising one or more pharmaceutically acceptable carriers and/or diluents.

This invention also extends to methods of use of the novel receptor-type tyrosine kinase of this invention and of antagonists to ligands binding to this tyrosine kinase.

In one aspect, this invention extends to a method of ameliorating the effects of interaction or binding between HEK and its ligand in a mammal comprising administering to said mammal an effective amount of the antagonist to a ligand binding to the tyrosine kinase of this invention.

The invention also extends to a method of phosphorylating a protein comprising contacting a preparation of said protein with an effective amount of the receptor-type tyrosine kinase of this invention for a time and under conditions sufficient to effect phosphorylation of the protein.

In yet another aspect, the invention provides a method of screening for a ligand bound to tissue or cells to the receptor-type tyrosine kinase of this invention comprising contacting the tyrosine kinase fused to a reporter molecule capable of producing a detectable signal to the tissue or cell sample to be tested for a time and under conditions sufficient for the fused tyrosine kinase to bind to a ligand on said tissue or cells and then detecting the reporter molecule.

The invention further provides a method of screening for a soluble ligand to the receptor-type tyrosine kinase of this invention comprising contacting a sample to be tested with a cell line capable of expressing the tyrosine kinase and screening for phosphorylation in said cell line.

One skilled in the art will, however, immediately recognise that a variety of mutations, derivatives or chemical alternations can be made to the sequence to encode, for example, the analogues and derivatives disclosed above. The present invention also extends to short nucleic acid molecules which can act as nucleic acid probes to screen for the presence of the HEK gene or mutations therein.

The present invention is further described with reference to the following non-limiting Figures and Examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1i represent the nucleotide sequence SEQ ID NO:9 and deduced amino acid sequence SEQ ID NO:10 of HEK coding sequence with partial 3' and 5' untranslated sequence. Numbers at right indicate positions of nucleotides and numbers above amino acids refer to amino acid sequence. A single underline indicates the presumed signal peptide. Double underline indicates the presumed transmembrane region. Dashed overline indicates identity between the predicted amino acid sequence and the sequence obtained from purified HEK protein. Triangles indicate potential sites for N-linked glycosylation within the extra-cellular domain. Dots indicate the putative ATP-binding site. The diamond indicates a putative autophosphorylation site. Asterisks indicate stop codons.

FIGS. 2a-2f represent the protein sequence alignment of HEK with elk SEQ ID NO:11, a related gene within the eph/elk family. Alignment was performed using the GAP programme. Amino acid positions are numbered on the right. Dots in the sequence indicate gaps introduced to optimise the alignment. Dashes indicate identity between amino acids. Asterisks indicate stop codons. Dots above the line of amino acids indicates residues contributing to the two repeats of homology with fibronectin type III, within the C-terminal regions of the extracellular domains. Triangles above the line of amino acids highlight conserved cyseine residues within the N-terminal region.

FIGS. 3a and 3b are photographic representations showing expression of HEK in COS cells. The HEK 4.5 kb cDNA clone was subcloned into the expression vector CDM8. COS cells were transfected with this construct using DEAE-dextran/chloroquine and DMSO. Two days after transfection cells were stained in situ with the IIIA4 MAb followed by FITC-conjugated sheep anti-mouse Ig and photographed under light microscopy (panel A), or fluorescence microscopy (panel B). Magnification ×400.

FIG. 4 is a photographic representation of Northern blot analysis of HEK expression in cell lines. Poly (A)+RNA from human cell lines was fractionated on an agarose/formaldehyde gel and transferred onto Hybond-C extra membrane. The filter was hybridised with the HEK 4.5 kb cDNA (upper panel). The same filter was hybridised with GAPDH as a quantitative control (lower panel). REH, NALM-1 and FAKEM are pre-B leukaemic cell lines. BALL-1 is an early B leukaemic cell line. RAMOS is a mature B leukaemic cell line. HSB-2, HPB-ALL and JM are T leukaemic cell lines.

FIG. 5 is a photographic representation showing Northern blot analysis of HEK expression in cell lines. Poly A⁺ RNA from human cell lines was probed for HEK expression as above. Molt 4 is an immature T cell line. RC2a, HL60 and U937 are myelomonocytic cell lines. In this experiment, RNA was extracted from HL60 and U937 after treatment of cells with tetra decannoyl phorbol myristic acetate (TPA), an activator of protein kinase C. U266 is a mature B cell line.

FIG. 6 is a photographic representation showing Northern analysis of HEK expression in adult post mortem tissues. A multiple tissue Northern blot was purchased commercially and probed for HEK expression under conditions suggested by the manufactuerer (Clontech). The 1.3 kb band in pancreas is too small to represent a transcript for a secreted form of HEK and is probably due to cross hybridisation.

FIG. 7 is a photographic representation showing Southern blot analysis of HEK in cell lines and normal human peripheral blood cell DNA. Samples were digested with Hind III (lanes 1-3) or Bam HI (lanes 4-6), run on a 1% agarose gel and transferred to Zetaprobe membrane. The membrane was hybridised with a 1.1 kb fragment of HEK extending from nucleotides 1,109 to 2,241 (see FIG. 1). Lanes 1 and 4, normal peripheral blood; Lanes 2 and 5, LK63 cells; lanes 3 and 6, LK63/CD20+ cells.

FIGS. 8a-8c are photographic representations showing in situ hybridisation. The ˜1.1 kb HEK PCR product referred to above was nick translated with biotin-14-dATP and hybridised in situ at a probe concentration of 5 ng/μl to metaphases from two normal males. Chromosomes were stained before analysis with both propidium iodide (as counterstain) and DAPI (for chromosome identification).

FIG. 9 is a graphical representation showing a hydropathy analysis (span length: 25) of the predicted translational product of the HEK 4.5 cDNA. The Y axis indicates a hydropathy index, with hydrophobic residues appearing above the origin and hydrophilic residues below. The AAs comprising the translated product of the HEK cDNA are numbered along the X axis from 1-983.

EXAMPLE 1. Materials and Methods

Cell lines, Mab III4 HEK protein structure and function

The LK63 and LK63/CD20+ cell lines were derived from a child with acute lymphoblastic leukaemia. LK63/CD20+ is a tetraploid variant of LK63, which arose spontaneously in vitro and has enhanced HEK expression. In contrast to the parental cell line, LK63/CD20+ expresses CD20. These lines have cytogenetic features of pre-B cell leukaemia and have not been transformed with Epstein-Barr virus (24). JM and HSB-2 are CD8+, human T cell leukaemic cell lines.

The IIIA4 Mab was generated against the LK63 cell line and recognised a 135 kD, cell surface molecule (HEK) with in vitro kinase activity expressed by LK63, LK63/CD20+ and JM (25).

The IIIA4 Mab was used to purify HEK antigen for amino acid sequencing (25). The amino acid sequences obtained were as follows, where doubtful residues are bracketed and unidentified residues are marked X: N terminus--SEQ ID NO:3 ELIPQPSNEVNLXD(S)KXIQ; internal--GYRLPPPMDCPAALYQLMLDC.

LK63 cDNA library construction and screening

A random primed cDNA library was constructed in λgt10 (Amersham) using 5 ug of poly A+ selected mRNA from LK63/CD20+ cells. A degenerate oligonucleotide was designed on the basis of the internal (3') HEK protein sequence. The neutral base inosine was included at positions of high codon degeneracy (26). The 51 mer: SEQ ID NO:5 ##STR1## was end labelled using γ32P-deoxyadenosine triphosphate (ATP) and polynucleotide kinase, followed by separation on a G25 Sephadex column as previously described (27). Approximately 250,000 plaques were screened in 2×SSC (SSC=0.15M NaCl, 0.015M sodium citrate) hybridisation buffer at 37°, as previously described (27). Washes were performed in 2×SSC/0.1% w/v sodium dodecyl sulphate (SDS) at 42°-55°. The signal from one duplicating plaque persisted following 55° washes. The DNA from this plaque contained an insert of 2.5 kb (HEK 2.5). HEK 2.5 was labelled with α³² P-ATP (Amersham random primer kit) for Northern blot analysis of LK63 cells. The polymerase chain reaction (PCR) was performed using HEK 2.5 and oligonucleotide primers based on conserved motifs within the catalytic domain of PTKs and the 3' amino acid HEK sequence, as previously described (28). HEK 2.5 was labelled with α³² P-ATP (as above) and used to rescreen the random primed LK63 cDNA library in 2×SSC hybridisation buffer at 65°. Thirty two duplicating positives were isolated and screened by hybridisation with a degenerate oligonucleotide based on the N terminal HEK protein sequence. A 4.5 kb HEK clone (HEK 4.5) which hybridised with the N terminal oligonucleotide was chosen for complete characterisation.

DNA sequencing and analysis of HEK cDNA

HEK 4.5 was subcloned into pGEM7 which had been digested with EcoRI and treated with calf intestinal phosphatase. Double stranded DNA was purified on a caesium chloride gradient and used as the template in dideoxy chain termination sequence reactions (29). Sense and antisense oligonucleotide primers were used to complete sequencing with T7 DNA polymerase (Promega). Protein sequence alignment was performed using the GAP programme (University of Wisconsin, Genetics Computer Group).

Expression of HEK in COS cells

The HEK 4.5 EcoRI insert was blunt ended with Klenow DNA polymerase 1 and dATP plus dTTP, followed by ligation to BstXI adaptors. The adapted insert was ligated to BstXI digested CDM8 (30). Sense and antisense constructs were prepared and transfected into COS cells using DEAE-dextran/chloroquine with dimethyl sulphoxide (DMSO) (17). Two days post-transfection, COS cells were stained with IIIA4 followed by fluorescein isothiocyanate conjugated (FITC)-conjugated sheep anti-mouse immunoglobulin (Ig) (Silenus) and examined under a fluorescence microscope.

Northern and Southern blot analysis of cell lines

Poly A+ selected mRNA was isolated as previously described (31) and fractionated on a 1% formaldehyde agarose gel prior to transfer onto a HybondC extra membrane (Amersham). Filters were probed with HEK 4.5 and subsequently with a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) insert as a control. DNA was prepared by lysis with guanidine hydrochloride (32), transferred to Zetaprobe membranes and hybridised under conditions suggested by the manufacturer (Bio-Rad). In order to minimise cross hybridisation with other tyrosine kinases in Southern analysis of genomic DNA, PCR was used to generate a 1.1 kb HEK probe which spans a less highly conserved region of the molecule (nucleotides 1,109 to 2,241, FIG. 1). The autoradiogram of the Southern blot was digitised using the MacScan programme on a Macintosh IIx computer.

Scatchard analysis of IIIA4 binding to cell lines

Binding of ¹²⁵ I labelled IIIA4 to cell lines was performed in competition with unlabelled IIIA4 as previously described (33).

Protein analysis

The HEK protein was subjected to hydrophobicity analysis as described by Kyte and Doolittle (40). The results are shown in FIG. 9.

Oligos to construct expression vectors encoding variants of the extracellular domain of HEK

Primer HEK5'/92 has the following sequence: SEQ ID NO:6 ##STR2##

The BamH1 and Eco R1 sites are indicated above the sequence and the underlined portion corresponds to positions 86 to 102 of the sequence set forth in FIG. 1.

Primer HEK/EE14/92 has the sequence: SEQ ID NO:7 ##STR3##

The underlined portion after the stop codon is the reversed and complemented sequence of nucleotide 1710-1725 of FIG. 1. ##STR4##

The underlined sequence when reversed and complemented corresponds to 1708-1723 of the sequence in FIG. 1 and does not contain the stop codon permitting read through from the BamH1 site.

PCR Conditions

PCR was performed with Taq polymerase under standard conditions using CsCl purified pGEM7-HEK; which contains the full length HEK cDNA, as a template. Cycle times and temperatures:

60' at 97° C.

60' at 55° C.

90' at 73° C.

the reaction was carried out for ten cycles.

1. The 1.7 kb PCR product of the HEK5'/92 and HEK/EE14/92 was purified using Geneclean, digested with Eco R1 and BamH1 and cloned between the Eco R1 and Bcl I site of pEE14 (obtained from Celltech, Berkshire, UK).

Analysis showed the predicted 1.7 kb insert in the clones which were designated "pEE14-HEK".

2. The 1.7 kb PCR product of 5' HEK5'/92 and HEK/TAG/3' was digested with BamH1, cloned into BglII site of AP-Tag-1, Flanagan & Leder (39). Using SnaB1, the sense of the clones could be determined to fused clones with the correct orientation. The resulting clones were designated AP-TAG-HEK

Expression

pEE14-HEK was transfected into CHO cells and lines selected with methionine sulfoxime.

AP-TAG-HEK was transfected into 3T3 cells with pSV2 neo and clones selected with G418.

EXAMPLE 2. HEK

Isolation and characterisation of cDNA clones for HEK

One duplicating signal was obtained from screening approximately 250,000 plaques of an LK63-derived λgt10 cDNA library under relaxed conditions with a degenerate 51 mer oligonucleotide. This plaque contained a 2.5 kb insert (HEK2.5) which hybridised with a single 5.5-6.0 kb mRNA species in Northern blot analysis of cell lines expressing HEK i.e. LK63 and JM. PCR using HEK 2.5 and oligonucleotide primers based on conserved motifs within the catalytic domains of tyrosine kinases (28), gave DNA products of the appropriate size. These results indicated HEK 2.5 was truncated at the 5' end. HEK 2.5 was used to re-screen the library under more stringent conditions and a 4.5 kb HEK (HEK 4.5) clone isolated. This clone hybridised with a degenerate oligonucleotide based on the N terminal protein sequence and produced DNA bands of the predicted sizes in PCR reactions using the primers referred to above. These data indicated the 4.5 kb clone probably contained the complete HEK coding region.

The sequence of the coding region for HEK together with partial 3' and 5' untranslated sequence, is shown in FIG. 1. An open reading frame of 2,952 nucleotides extends from the initiation methionine at position 100 to the first termination codon at position 3051. Translation of the cDNA results in a predicted protein of 983 amino acids (AAs). There is identity between the AAs obtained by sequencing of purified HEK protein and the predicted AA product of the cDNA clone (see FIG. 1). The predicted molecular weight of the translated protein (minus the putative signal peptide) is 92.8 kD. This is in good agreement with previous results demonstrating a core protein of approximately 95 kD in both tunicamycin- and endoglycosidase-treated LK63 cells (25). The predicted protein product of the HEK cDNA clone has the features of a type 1a integral membrane protein (35). Two predominantly hydrophobic regions indiciate a putative signal peptide (AAs 1-20) and a transmembrane segment (AAs 542-565). The extracellular domain of 521 AAs contains five possible sites for N linked glycosylation. The N terminal region (AAs 21-376) of the extracellular domain is rich in cysteine residues. The C-terminal region (AAs 326-511) of the extracellular domain contains two repeats homologous to those found in fibronectin type III (36). The cytoplasmic domain (AAs 566-983) of HEK contains a typical ATP binding site (GXGXXG; SEQ ID NO:12) at AA positions 628-633 and a putative autophosphorylation site (E/DXXYXX; SEQ ID NOS:13,14) at position 779.

Protein sequence alignment shows a high degree of homology between HEK and eph, elk, eck, eek and erk in the catalytic domains. HEK has the following overall protein sequence homology with each of the three sequenced members of the eph RTK family: (chicken) CEK 56.4%, (rat) elk 56.1%; (rat) eck 50.6%; (human) eph 42.3%. Protein sequence alignment between HEK and a close relative ELK is shown in FIG. 2. The homology between these molecules is greatest within the catalytic domains. Outside the catalytic domains, numerous short motifs which may be of structural or functional significance, are conserved between HEK, eph, elk and eck, particularly towards the N terminus. There is strict conservation of the number and spatial arrangement of cysteine residues within the extracellular domains of HEK, eph, elk and eck (34). These cytokine residues cluster within the N terminal portion of the extracellular domains (36). The C terminal regions of the extracellular domains contain repeats which are homologous to those found in fibronectin type III (36). HEK has a cysteine in the C terminal tail (AA928), rather than the tyrosine which is conserved in this position between other members of the EPH/ELK family. This may be of significance in that phosphorylation of C terminal tyrosine residues can regulate tyrosine kinase activity (37). However HEK has a C terminal tyrosine at position 937, which also appears to be in a better context for autophosphorylation (38).

Transfection and expression of HEK in COS cells

To demonstrate that the cDNA clone isolated did indeed encode the molecule recognised by the IIIA4 Mab, HEK 4.5 was subcloned into the expression vector CDM8 and transfected into COS cells in both sense and antisense orientations. As shown in FIG. 3, COS cells transfected with HEK in the sense orientation stained specifically with IIIA4, confirming that the cDNA clone contains the full coding sequence and is identical to the molecule recognised by IIIA4. COS cells transfected with HEK in the antisense orientation did not stain with IIIA4.

Expression of HEK in human lymphoid cell lines

Cell surface staining with IIIA4 revealed a highly restricted pattern of HEK expression on LK63--a pre B cell line, and JM--a T cell line. To further explore the expression of HEK, Northern blot analysis was performed with HEK 4.5 (FIGS. 4 to 6). A single 5.5-6.0 kb band was seen in both LK63 and JM cells. However there was a less intense band of the same size in another T cell line--HSB-2--which did not stain with IIIA4. Other cell lines in which HEK transcripts were detected include Lila-1, MOIT4 and HeLa. There were no HEK transcripts detected in a range of other cell lines although a weak band was seen in heart muscle (FIG. 6). The number of HEK molecules was determined on HSB-2, LK63/CD20+ and other cells using Scatchard analysis of IIIA4 MAb binding. The LK63/CD20+ cells had approximately 15,000 sites per cell and JM cells had 9,500 sites per cell. In contrast, HSB-2 had approximately 1,070 sites per cell, which is too low for detection by immunofluorescence against the autofluorescence background of this cell line. The affinity constants for antibody binding were in the range of 2.5-4.0×10⁹. Raji and K562 cells showed no detectable antibody binding above background. Tables 1 and 2 summarise the phenotype of HEK expression cell lines.

Southern blot analysis

To investigate the basis for overexpression of HEK in the lymphoid tumour cell line LK63, Southern analysis of genomic DNA was performed (FIG. 7). A 1.1 kb fragment covering a less conserved region of HEK (see above), was used as a probe in order to minimise background arising from conserved regions of the catalytic domains of related tyrosine kinase molecules. Compared with normal peripheral blood mononuclear cell DNA, there is no apparent amplification or rearrangement of the HEK gene in the LK63 or LK63/CD20+ tumour cell lines.

Chromosomal assignment of HEK

HEK cDNA was used as a probe to locate the position of the HEK gene within the normal human chromosome complement. Chromosomal assignment was performed in two ways--by in situ hybridisation and by Southern analysis of somatic cell hybrids. Thirty normal male metaphases were examined for a fluorescent signal: Twenty four of these metaphases showed signal on one or both chromatids of chromosome 3 in the region of 3cen→3p12.1. 85% of this signal was at 3p11.2 (FIG. 8). There were a total of nine non-specific background dots observed in these 30 metaphases. Similar results were obtained from the hybridisation to the second male. Southern blot analysis of the hybrid cell panel showed hybridisation of the HEK probe only to hybrids containing material from human chromosome 3. Bands of 5.2, 4.8, 4.3, 2.4 and 1.9 kb were obtained from the Hind III digest and bands of 4.3, 3.2 and 1.9 kb were obtained from the Taq1 digest. The hybrid cell panel used represents the entire human genome except for chromosomes 2, 6q, 8, 11p and Y. The results from both techniques thus localised the HEK gene to chromosome 3 and in situ hybridisation analysis positioned this more precisely to 3p11.2. This region was not cytogenetically abnormal in HEK-positive tumours. Similarly, there was no isolated change in the copy number of chromosome 3 in HEK-positive cell lines and no isochromosome formation involving chromosome 3.

                                      TABLE 1                                      __________________________________________________________________________     Phenotype of HEK-positive human lymphoid cell lines.                           The phenotype of HEK-positive cell lines was determined by staining for T      and                                                                            B cell markers followed by FACS analysis. + weakly positive,                   ++ positive,                                                                   +++ strongly positive.                                                         ILA4   IgM CD19                                                                              CD20                                                                               CD1                                                                               CD2 CD3                                                                               CD4 CD7                                                                               CD8                                         __________________________________________________________________________     LK63                                                                               ++ +   +  -   -  -   -  -   -  -                                           LK63T                                                                              +++                                                                               ++  ++ ++  -  -   -  -   -  -                                           Lila-1                                                                             -  +   ++ -   -  -   -  -   -  -                                           HSB-2  -   -  -   -  -   +      ++                                             JM  +  -   -  -   +  -   +  ++  ++ ++                                          Molt4                                                                              -  -   -  -   +  ++  -  -   ++ +                                           __________________________________________________________________________

                  TABLE 2                                                          ______________________________________                                         Summary of HEK expression in human cell lines                                  HEK-positive cell lines were characterised using a combination of cell         surface staining, Northern blot analysis and Scatchard analysis. +             weakly                                                                         positive, ++ positive, +++ strongly positive. NT, not tested.                  Line      Lineage ILA4/IF   Receptors/cell                                                                          RNA                                       ______________________________________                                         LK63      Pre-B   ++        15,000   ++                                        LK63T     Pre-B   +++       NT       +++                                       Lila      Pre-B   -         NT       +                                         JM        T cell  ++        9,500    ++                                        HSB-2     T cell  -         1,100    +                                         Molt 4    T cell  -         NT       +                                         HeLa      Cervical                                                                               -         NT       +                                         ______________________________________                                    

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

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    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 14                                                  (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        GluLeuIleProGlnPro                                                             15                                                                             (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 14 amino acids                                                     (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        GluLeuIleProGlnProSerAsnGluValAsnLeuXaaAsp                                     1510                                                                           (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 19 amino acids                                                     (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        GluLeuIleProGlnProSerAsnGluValAsnLeuXaaAspSerLys                               151015                                                                         XaaIleGln                                                                      (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 21 amino acids                                                     (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        GlyTyrArgLeuProProProMetAspCysProAlaAlaLeuTyrGln                               151015                                                                         LeuMetLeuAspCys                                                                20                                                                             (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 51 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 6..7                                                             (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 9..10                                                            (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 12..13                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 15..16                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 18..19                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 30..31                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 33..34                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 36..37                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 39..40                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (ix) FEATURE:                                                                  (A) NAME/KEY: modified.sub.-- base                                             (B) LOCATION: 48..49                                                           (D) OTHER INFORMATION: /mod.sub.-- base=i                                      (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        TACCGNCTNCCNCCNCCNATGGACTGCCCNGCNGCNCTNTACCAACTNATG51                          (2) INFORMATION FOR SEQ ID NO:6:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 31 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                        GTAGGGATCCGAATTCTGCACCAGCAACATG31                                              (2) INFORMATION FOR SEQ ID NO:7:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 28 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                        GTAGGGATCCTACACTTGGCTACTTTCA28                                                 (2) INFORMATION FOR SEQ ID NO:8:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 24 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                        GCGGATCCTTGCCTACTTTCACCA24                                                     (2) INFORMATION FOR SEQ ID NO:9:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 3132 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 100..3048                                                        (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                        CATGGATGGTAACTTCTCCAGCAATCAGAGCGCTCCCCCTCACATCAGTGGCATGCTTCA60                 TGGAGATATGCTCCTCTCACTGCCCTCTGCACCAGCAACATGGATTGTCAGCTC114                      MetAspCysGlnLeu                                                                15                                                                             TCCATCCTCCTCCTTCTCAGCTGCTCTGTTCTCGACAGCTTCGGGGAA162                            SerIleLeuLeuLeuLeuSerCysSerValLeuAspSerPheGlyGlu                               101520                                                                         CTGATTCCGCAGCCTTCCAATGAAGTCAATCTACTGGATTCAAAAACA210                            LeuIleProGlnProSerAsnGluValAsnLeuLeuAspSerLysThr                               253035                                                                         ATTCAAGGGGAGCTGGGCTGGATCTCTTATCCATCACATGGGTGGGAA258                            IleGlnGlyGluLeuGlyTrpIleSerTyrProSerHisGlyTrpGlu                               404550                                                                         GAGATCAGTGGTGTGGATGAACATTACACACCCATCAGGACTTACCAG306                            GluIleSerGlyValAspGluHisTyrThrProIleArgThrTyrGln                               556065                                                                         GTGTGCAATGTCATGGACCACAGTCAAAACAATTGGCTGAGAACAAAC354                            ValCysAsnValMetAspHisSerGlnAsnAsnTrpLeuArgThrAsn                               70758085                                                                       TGGGTCCCCAGGAACTCAGCTCAGAAGATTTATGTGGAGCTCAAGTTC402                            TrpValProArgAsnSerAlaGlnLysIleTyrValGluLeuLysPhe                               9095100                                                                        ACTCTACGAGACTGCAATAGCATTCCATTGGTTTTAGGAACTTGCAAG450                            ThrLeuArgAspCysAsnSerIleProLeuValLeuGlyThrCysLys                               105110115                                                                      GAGACATTCAACCTGTACTACATGGAGTCTGATGATGATCATGGGGTG498                            GluThrPheAsnLeuTyrTyrMetGluSerAspAspAspHisGlyVal                               120125130                                                                      AAATTTCGAGAGCATCAGTTTACAAAGATTGACACCATTGCAGCTGAT546                            LysPheArgGluHisGlnPheThrLysIleAspThrIleAlaAlaAsp                               135140145                                                                      GAAAGTTTCACTCAAATGGATCTTGGGGACCGTATTCTGAAGCTCAAC594                            GluSerPheThrGlnMetAspLeuGlyAspArgIleLeuLysLeuAsn                               150155160165                                                                   ACTGAGATTAGAGAAGTAGGTCCTGTCAACAAGAAGGGATTTTATTTG642                            ThrGluIleArgGluValGlyProValAsnLysLysGlyPheTyrLeu                               170175180                                                                      GCATTTCAAGATGTTGGTGCTTGTGTTGCCTTGGTGTCTGTGAGAGTA690                            AlaPheGlnAspValGlyAlaCysValAlaLeuValSerValArgVal                               185190195                                                                      TACTTCAAAAAGTGCCCATTTACAGTGAAGAATCTGGCTATGTTTCCA738                            TyrPheLysLysCysProPheThrValLysAsnLeuAlaMetPhePro                               200205210                                                                      GACACGGTACCCATGGACTCCCAGTCCCTGGTGGAGGTTAGAGGGTCT786                            AspThrValProMetAspSerGlnSerLeuValGluValArgGlySer                               215220225                                                                      TGTGTCAACAATTCTAAGGAGGAAGATCCTCCAAGGATGTACTGCAGT834                            CysValAsnAsnSerLysGluGluAspProProArgMetTyrCysSer                               230235240245                                                                   ACAGAAGGCGAATGGCTTGTACCCATTGGCAAGTGTTCCTGCAATGCT882                            ThrGluGlyGluTrpLeuValProIleGlyLysCysSerCysAsnAla                               250255260                                                                      GGCTATGAAGAAAGAGGTTTTATGTGCCAAGCTTGTCGACCAGGTTTC930                            GlyTyrGluGluArgGlyPheMetCysGlnAlaCysArgProGlyPhe                               265270275                                                                      TACAAGGCATTGGATGGTAATATGAAGTGTGCTAAGTGCCCGCCTCAC978                            TyrLysAlaLeuAspGlyAsnMetLysCysAlaLysCysProProHis                               280285290                                                                      AGTTCTACTCAGGAAGATGGTTCAATGAACTGCAGGTGTGAGAATAAT1026                           SerSerThrGlnGluAspGlySerMetAsnCysArgCysGluAsnAsn                               295300305                                                                      TACTTCCGGGCAGACAAAGACCCTCCATCCATGGCTTGTACCCGACCT1074                           TyrPheArgAlaAspLysAspProProSerMetAlaCysThrArgPro                               310315320325                                                                   CCATCTTCACCAAGAAATGTTATCTCTAATATAAACGAGACCTCAGTT1122                           ProSerSerProArgAsnValIleSerAsnIleAsnGluThrSerVal                               330335340                                                                      ATCCTGGACTGGAGTTGGCCCCTGGACACAGGAGGCCGGAAAGATGTT1170                           IleLeuAspTrpSerTrpProLeuAspThrGlyGlyArgLysAspVal                               345350355                                                                      ACCTTCAACATCATATGTAAAAAATGTGGGTGGAATATAAAACAGTGT1218                           ThrPheAsnIleIleCysLysLysCysGlyTrpAsnIleLysGlnCys                               360365370                                                                      GAGCCATGCAGCCCAAATGTCCGCTTCCTCCCTCGACAGTTTGGACTC1266                           GluProCysSerProAsnValArgPheLeuProArgGlnPheGlyLeu                               375380385                                                                      ACCAACACCACGGTGACAGTGACAGACCTTCTGGCACATACTAACTAC1314                           ThrAsnThrThrValThrValThrAspLeuLeuAlaHisThrAsnTyr                               390395400405                                                                   ACCTTTGAGATTGATGCCGTTAATGGGGTGTCAGAGCTGAGCTCCCCA1362                           ThrPheGluIleAspAlaValAsnGlyValSerGluLeuSerSerPro                               410415420                                                                      CCAAGACAGTTTGCTGCGGTCAGCATCACAACTAATCAGGCTGCTCCA1410                           ProArgGlnPheAlaAlaValSerIleThrThrAsnGlnAlaAlaPro                               425430435                                                                      TCACCTGTCCTGACGATTAAGAAAGATCGGACCTCCAGAAATAGCATC1458                           SerProValLeuThrIleLysLysAspArgThrSerArgAsnSerIle                               440445450                                                                      TCTTTGTCCTGGCAAGAACCTGAACATCCTAATGGGATCATATTGGAC1506                           SerLeuSerTrpGlnGluProGluHisProAsnGlyIleIleLeuAsp                               455460465                                                                      TACGAGGTCAAATACTATGAAAAGCAGGAACAAGAAACAAGTTATACC1554                           TyrGluValLysTyrTyrGluLysGlnGluGlnGluThrSerTyrThr                               470475480485                                                                   ATTCTGAGGGCAAGAGGCACAAATGTTACCATCAGTAGCCTCAAGCCT1602                           IleLeuArgAlaArgGlyThrAsnValThrIleSerSerLeuLysPro                               490495500                                                                      GACACTATATACGTATTACAAATCCGAGCCCGAACAGCCGCTGGATAT1650                           AspThrIleTyrValLeuGlnIleArgAlaArgThrAlaAlaGlyTyr                               505510515                                                                      GGGACGAACAGCCGCAAGTTTGAGTTTGAAACTAGTCCAGACTCTTTC1698                           GlyThrAsnSerArgLysPheGluPheGluThrSerProAspSerPhe                               520525530                                                                      TCCATCTCTGGTGAAAGTAGCCAAGTGGTCATGATCGCCATTTCAGCG1746                           SerIleSerGlyGluSerSerGlnValValMetIleAlaIleSerAla                               535540545                                                                      GCAGTAGCAATTATTCTCCTCACTGTTGTCATCTATGTTTTGATTGGG1794                           AlaValAlaIleIleLeuLeuThrValValIleTyrValLeuIleGly                               550555560565                                                                   AGGTTCTGTGGCTATAAGTCAAAACATGGGGCAGATGAAAAAAGACTT1842                           ArgPheCysGlyTyrLysSerLysHisGlyAlaAspGluLysArgLeu                               570575580                                                                      CATTTTGGCAATGGGCATTTAAAACTTCCAGGTCTCAGGACTTATGTT1890                           HisPheGlyAsnGlyHisLeuLysLeuProGlyLeuArgThrTyrVal                               585590595                                                                      GACCCACATACATATGAAGACCCTACCCAAGCTGTTCATGAGTTTGCC1938                           AspProHisThrTyrGluAspProThrGlnAlaValHisGluPheAla                               600605610                                                                      AAGGAATTGGATGCCACCAACATATCCATTGATAAAGTTGTTGGAGCA1986                           LysGluLeuAspAlaThrAsnIleSerIleAspLysValValGlyAla                               615620625                                                                      GGTGAATTTGGAGAGGTGTGCAGTGGTCGCTTAAAACTTCCTTCAAAA2034                           GlyGluPheGlyGluValCysSerGlyArgLeuLysLeuProSerLys                               630635640645                                                                   AAAGAGATTTCAGTGGCCATTAAAACCCTGAAAGTTGGCTACACAGAA2082                           LysGluIleSerValAlaIleLysThrLeuLysValGlyTyrThrGlu                               650655660                                                                      AAGCAGAGGAGAGACTTCCTGGGAGAAGCAAGCATTATGGGACAGTTT2130                           LysGlnArgArgAspPheLeuGlyGluAlaSerIleMetGlyGlnPhe                               665670675                                                                      GACCACCCCAATATCATTCGACTGGAAGGAGTTGTTACCAAAAGTAAG2178                           AspHisProAsnIleIleArgLeuGluGlyValValThrLysSerLys                               680685690                                                                      CCAGTTATGATTGTCACAGAATACATGGAGAATGGTTCCTTGGATAGT2226                           ProValMetIleValThrGluTyrMetGluAsnGlySerLeuAspSer                               695700705                                                                      TTCCTACGTAAACACGATGCCCAGTTTACTGTCATTCAGCTACTGGGG2274                           PheLeuArgLysHisAspAlaGlnPheThrValIleGlnLeuLeuGly                               710715720725                                                                   ATGCTTCGAGGGATAGCATCTGGCATGAAGTACCTGTCAGACATGGGC2322                           MetLeuArgGlyIleAlaSerGlyMetLysTyrLeuSerAspMetGly                               730735740                                                                      TATGTTCACCGAGACCTCGCTGCTCGGAACATCTTGATCAACAGTAAC2370                           TyrValHisArgAspLeuAlaAlaArgAsnIleLeuIleAsnSerAsn                               745750755                                                                      TTGGTGTGTAAGGTTTCTGATTTCGGACTTTCGCGTGTCCTGGAGGAT2418                           LeuValCysLysValSerAspPheGlyLeuSerArgValLeuGluAsp                               760765770                                                                      GACCCAGAAGCTGCTTATACAACAAGAGGAGGGAAGATCCCAATCAGG2466                           AspProGluAlaAlaTyrThrThrArgGlyGlyLysIleProIleArg                               775780785                                                                      TGGACATCACCAGAAGCTATAGCCTACCGCAAGTTCACGTCAGCCAGC2514                           TrpThrSerProGluAlaIleAlaTyrArgLysPheThrSerAlaSer                               790795800805                                                                   GATGTATGGAGTTATGGGATTGTTCTCTGGGAGGTGATGTCTTATGGA2562                           AspValTrpSerTyrGlyIleValLeuTrpGluValMetSerTyrGly                               810815820                                                                      GAGAGACCATACTGGGAGATGTCCAATCAGGATGTAATTAAAGCTGTA2610                           GluArgProTyrTrpGluMetSerAsnGlnAspValIleLysAlaVal                               825830835                                                                      GATGAGGGCTATCGACTGCCACCCCCCATGGACTGCCCAGCTGCCTTG2658                           AspGluGlyTyrArgLeuProProProMetAspCysProAlaAlaLeu                               840845850                                                                      TATCAGCTGATGCTGGACTGCTGGCAGAAAGACAGGAACAACAGACCC2706                           TyrGlnLeuMetLeuAspCysTrpGlnLysAspArgAsnAsnArgPro                               855860865                                                                      AAGTTTGAGCAGATTGTTAGTATTCTGGACAAGCTTATCCGGAATCCC2754                           LysPheGluGlnIleValSerIleLeuAspLysLeuIleArgAsnPro                               870875880885                                                                   GGCAGCCTGAAGATCATCACCAGTGCAGCCGCAAGGCCATCAAACCTT2802                           GlySerLeuLysIleIleThrSerAlaAlaAlaArgProSerAsnLeu                               890895900                                                                      CTTCTGGACCAAAGCAATGTGGATATCTCTACCTTCCGCACAACAGGT2850                           LeuLeuAspGlnSerAsnValAspIleSerThrPheArgThrThrGly                               905910915                                                                      GACTGGCTTAATGGTGTCCGGACAGCACACTGCAAGGAAATCTTCACG2898                           AspTrpLeuAsnGlyValArgThrAlaHisCysLysGluIlePheThr                               920925930                                                                      GGCGTGGAGTACAGTTCTTGTGACACAATAGCCAAGATTTCCACAGAT2946                           GlyValGluTyrSerSerCysAspThrIleAlaLysIleSerThrAsp                               935940945                                                                      GACATGAAAAAGGTTGGTGTCACCGTGGTTGGGCCACAGAAGAAGATC2994                           AspMetLysLysValGlyValThrValValGlyProGlnLysLysIle                               950955960965                                                                   ATCAGTAGCATTAAAGCTCTAGAAACGCAATCAAAGAATGGCCCAGTT3042                           IleSerSerIleLysAlaLeuGluThrGlnSerLysAsnGlyProVal                               970975980                                                                      CCCGTGTAAAGCACGACGGAAGTGCTTCTGGACGGAAGTGGTGGCTGTGGAAGGCG3098                   ProVal                                                                         TCAAGTCATCCTGCAGACAGACAATAATTCTGGA3132                                         (2) INFORMATION FOR SEQ ID NO:10:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 983 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:                                       MetAspCysGlnLeuSerIleLeuLeuLeuLeuSerCysSerValLeu                               151015                                                                         AspSerPheGlyGluLeuIleProGlnProSerAsnGluValAsnLeu                               202530                                                                         LeuAspSerLysThrIleGlnGlyGluLeuGlyTrpIleSerTyrPro                               354045                                                                         SerHisGlyTrpGluGluIleSerGlyValAspGluHisTyrThrPro                               505560                                                                         IleArgThrTyrGlnValCysAsnValMetAspHisSerGlnAsnAsn                               65707580                                                                       TrpLeuArgThrAsnTrpValProArgAsnSerAlaGlnLysIleTyr                               859095                                                                         ValGluLeuLysPheThrLeuArgAspCysAsnSerIleProLeuVal                               100105110                                                                      LeuGlyThrCysLysGluThrPheAsnLeuTyrTyrMetGluSerAsp                               115120125                                                                      AspAspHisGlyValLysPheArgGluHisGlnPheThrLysIleAsp                               130135140                                                                      ThrIleAlaAlaAspGluSerPheThrGlnMetAspLeuGlyAspArg                               145150155160                                                                   IleLeuLysLeuAsnThrGluIleArgGluValGlyProValAsnLys                               165170175                                                                      LysGlyPheTyrLeuAlaPheGlnAspValGlyAlaCysValAlaLeu                               180185190                                                                      ValSerValArgValTyrPheLysLysCysProPheThrValLysAsn                               195200205                                                                      LeuAlaMetPheProAspThrValProMetAspSerGlnSerLeuVal                               210215220                                                                      GluValArgGlySerCysValAsnAsnSerLysGluGluAspProPro                               225230235240                                                                   ArgMetTyrCysSerThrGluGlyGluTrpLeuValProIleGlyLys                               245250255                                                                      CysSerCysAsnAlaGlyTyrGluGluArgGlyPheMetCysGlnAla                               260265270                                                                      CysArgProGlyPheTyrLysAlaLeuAspGlyAsnMetLysCysAla                               275280285                                                                      LysCysProProHisSerSerThrGlnGluAspGlySerMetAsnCys                               290295300                                                                      ArgCysGluAsnAsnTyrPheArgAlaAspLysAspProProSerMet                               305310315320                                                                   AlaCysThrArgProProSerSerProArgAsnValIleSerAsnIle                               325330335                                                                      AsnGluThrSerValIleLeuAspTrpSerTrpProLeuAspThrGly                               340345350                                                                      GlyArgLysAspValThrPheAsnIleIleCysLysLysCysGlyTrp                               355360365                                                                      AsnIleLysGlnCysGluProCysSerProAsnValArgPheLeuPro                               370375380                                                                      ArgGlnPheGlyLeuThrAsnThrThrValThrValThrAspLeuLeu                               385390395400                                                                   AlaHisThrAsnTyrThrPheGluIleAspAlaValAsnGlyValSer                               405410415                                                                      GluLeuSerSerProProArgGlnPheAlaAlaValSerIleThrThr                               420425430                                                                      AsnGlnAlaAlaProSerProValLeuThrIleLysLysAspArgThr                               435440445                                                                      SerArgAsnSerIleSerLeuSerTrpGlnGluProGluHisProAsn                               450455460                                                                      GlyIleIleLeuAspTyrGluValLysTyrTyrGluLysGlnGluGln                               465470475480                                                                   GluThrSerTyrThrIleLeuArgAlaArgGlyThrAsnValThrIle                               485490495                                                                      SerSerLeuLysProAspThrIleTyrValLeuGlnIleArgAlaArg                               500505510                                                                      ThrAlaAlaGlyTyrGlyThrAsnSerArgLysPheGluPheGluThr                               515520525                                                                      SerProAspSerPheSerIleSerGlyGluSerSerGlnValValMet                               530535540                                                                      IleAlaIleSerAlaAlaValAlaIleIleLeuLeuThrValValIle                               545550555560                                                                   TyrValLeuIleGlyArgPheCysGlyTyrLysSerLysHisGlyAla                               565570575                                                                      AspGluLysArgLeuHisPheGlyAsnGlyHisLeuLysLeuProGly                               580585590                                                                      LeuArgThrTyrValAspProHisThrTyrGluAspProThrGlnAla                               595600605                                                                      ValHisGluPheAlaLysGluLeuAspAlaThrAsnIleSerIleAsp                               610615620                                                                      LysValValGlyAlaGlyGluPheGlyGluValCysSerGlyArgLeu                               625630635640                                                                   LysLeuProSerLysLysGluIleSerValAlaIleLysThrLeuLys                               645650655                                                                      ValGlyTyrThrGluLysGlnArgArgAspPheLeuGlyGluAlaSer                               660665670                                                                      IleMetGlyGlnPheAspHisProAsnIleIleArgLeuGluGlyVal                               675680685                                                                      ValThrLysSerLysProValMetIleValThrGluTyrMetGluAsn                               690695700                                                                      GlySerLeuAspSerPheLeuArgLysHisAspAlaGlnPheThrVal                               705710715720                                                                   IleGlnLeuLeuGlyMetLeuArgGlyIleAlaSerGlyMetLysTyr                               725730735                                                                      LeuSerAspMetGlyTyrValHisArgAspLeuAlaAlaArgAsnIle                               740745750                                                                      LeuIleAsnSerAsnLeuValCysLysValSerAspPheGlyLeuSer                               755760765                                                                      ArgValLeuGluAspAspProGluAlaAlaTyrThrThrArgGlyGly                               770775780                                                                      LysIleProIleArgTrpThrSerProGluAlaIleAlaTyrArgLys                               785790795800                                                                   PheThrSerAlaSerAspValTrpSerTyrGlyIleValLeuTrpGlu                               805810815                                                                      ValMetSerTyrGlyGluArgProTyrTrpGluMetSerAsnGlnAsp                               820825830                                                                      ValIleLysAlaValAspGluGlyTyrArgLeuProProProMetAsp                               835840845                                                                      CysProAlaAlaLeuTyrGlnLeuMetLeuAspCysTrpGlnLysAsp                               850855860                                                                      ArgAsnAsnArgProLysPheGluGlnIleValSerIleLeuAspLys                               865870875880                                                                   LeuIleArgAsnProGlySerLeuLysIleIleThrSerAlaAlaAla                               885890895                                                                      ArgProSerAsnLeuLeuLeuAspGlnSerAsnValAspIleSerThr                               900905910                                                                      PheArgThrThrGlyAspTrpLeuAsnGlyValArgThrAlaHisCys                               915920925                                                                      LysGluIlePheThrGlyValGluTyrSerSerCysAspThrIleAla                               930935940                                                                      LysIleSerThrAspAspMetLysLysValGlyValThrValValGly                               945950955960                                                                   ProGlnLysLysIleIleSerSerIleLysAlaLeuGluThrGlnSer                               965970975                                                                      LysAsnGlyProValProVal                                                          980                                                                            (2) INFORMATION FOR SEQ ID NO:11:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 432 amino acids                                                    (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:11:                                       MetAlaLeuLeuPheLeuAlaAlaValAlaAlaMetGluThrMetThr                               151015                                                                         ArgAlaThrAlaThrAlaAsnAlaSerValTyrTyrThrSerValIle                               202530                                                                         AlaThrLysSerAlaPheTrpSerAlaProTyrLeuValSerValPhe                               354045                                                                         GlyLeuMetValValSerPheLeuThrArgAlaGluValValIleLys                               505560                                                                         LeuAsnGlyAspMetArgThrLysProAsnSerValAlaLysProAla                               65707580                                                                       ThrPheSerGlnGluAlaGluGlySerHisSerAsnAsnLeuAsnThr                               859095                                                                         PheGluProAsnLeuThrPheIleAsnArgGlyHisArgThrMetArg                               100105110                                                                      ValSerLeuAsnProSerAsnTyrMetSerLeuPheSerIleGlnPhe                               115120125                                                                      ValGluMetThrGlyAlaGluThrIleAlaThrIleProArgSerPro                               130135140                                                                      SerGluAlaProIleThrArgThrGlyTyrPheGluValSerValGly                               145150155160                                                                   IleValIleGluHisProArgGluAspTyrArgAlaAspArgArgSer                               165170175                                                                      SerArgAspAspGluValLeuGluCysArgSerIleSerSerTrpPro                               180185190                                                                      AspGlnIleIleArgGluHisAsnPheAsnSerSerMetAlaSerGln                               195200205                                                                      ThrAsnThrAlaArgAspGlyArgGlyMetValValValValLysPhe                               210215220                                                                      GlyMetCysGlnLeuThrAspAspTyrLysMetLysIleIlePheAsn                               225230235240                                                                   GluArgIleValSerPheValLysGluGluIleTyrLysGlyArgTyr                               245250255                                                                      SerLysProPheProHisValSerAsnThrProIleMetHisGlnVal                               260265270                                                                      SerAlaThrMetArgThrProGlnGlnGluLeuArgGluLeuProLeu                               275280285                                                                      GlyAlaGlyValValPheValValSerLeuAlaSerIleValCysSer                               290295300                                                                      LysArgAlaSerLysGluAlaValTyrSerAspLeuGlnTyrSerThr                               305310315320                                                                   ArgGlySerAlaSerSerArgIlePheAlaGlnAsnGlyAlaGluAsn                               325330335                                                                      ValTyrGlnThrAsnIleGluGlnAspHisSerArgAlaGluAsnThr                               340345350                                                                      MetAlaSerGluLeuLeuArgIleLeuAlaHisLeuHisSerMetArg                               355360365                                                                      ValMetAsnGlnSerSerValMetAlaSerAspProThrSerSerLeu                               370375380                                                                      ValAlaMetPheAspThrValAlaThrIleThrValGlnProArgIle                               385390395400                                                                   ProPheThrAlaThrValAspSerAlaIleLysMetValGlnTyrArg                               405410415                                                                      AspSerLeuThrAlaGlyPheThrLeuGlnLeuValThrGlnMetThr                               420425430                                                                      (2) INFORMATION FOR SEQ ID NO:12:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12:                                       GlyXaaGlyXaaXaaGly                                                             15                                                                             (2) INFORMATION FOR SEQ ID NO:13:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13:                                       GluXaaXaaTyrXaaXaa                                                             15                                                                             (2) INFORMATION FOR SEQ ID NO:14:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 6 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:14:                                       AspXaaXaaTyrXaaXaa                                                             15                                                                             __________________________________________________________________________ 

We claim:
 1. A method of screening for a tissue- or cell-bound ligand to a receptor-type tyrosine kinase having the sequence of SEQ ID NO:10 comprising contacting a fusion protein comprising the extracellular domain of said tyrosine kinase fused to a reporter molecule that produces a detectable signal with the tissue or cell sample to be tested for a time and under conditions whereby said fusion protein binds to said tissue- or cell-bound ligand to form a ligand-fusion protein complex, removing said fusion protein that is not bound to said ligand, and then detecting the signal produced by said reporter molecule in said ligand-fusion protein complex.
 2. The method according to claim 1 wherein the reporter molecule is alkaline phosphatase.
 3. The method according to claim 1 or 2 wherein said fusion protein is encoded by AP-TAG-HEK.
 4. A method of screening for a soluble ligand to a receptor-type tyrosine kinase having the sequence of SEQ ID NO:10 comprising contacting a sample to be tested with a cell line that expresses said tyrosine kinase and screening for phosporylation in said cell line.
 5. The method according to claim 4 wherein the cell line is LK63 or a HEK transformant cell line.
 6. The method according to claim 4 or 5 wherein the sample is a supernatant fluid. 